Precision Fluid Dispensing Using Peristaltic Roller Control

ABSTRACT

A precision fluid dispensing system that can be effectively used for accurate fluid dispensing in peristaltic pumps if roller control is used. A peristaltic pump driven by a primary motor with a first encoder can be combined with pinch valves allowing a dispense tube to be open while a source tube is blocked. Controlled roller movement is used to move the next roller to the same starting position as the previous roller was on the previous dispense, the dispense pinch valve is closed and the source valve is opened. The system uses roller positioning where the each roller is properly positioned so that each dispense cycle starts in the same position. The precision and accuracy is better than 0.3% total. Tubing can be pre-stretched using a second motor and second encoder. Tube wear and stretch during use can be monitored by the second encoder.

This application is a continuation-in-part of application Ser. No.14/685,161 filed Apr. 13, 2015 which claimed priority from, U.S.Provisional Patent Application No. 61/978,911 filed Apr. 13, 2014.Application Ser. No. 14/685,161 and 61/978,911 are hereby incorporatedby reference in their entirety.

BACKGROUND Field of the Invention

The present invention relates to peristaltic pumps and more particularlyto a precision fluid dispensing using peristaltic roller control.

Description of the Prior Art

Peristaltic pumps find use for fluid dispensing in many fields wherepump contamination is a concern, aggressive fluids can be used, slurriesthat can pass through the peristaltic pump or minimizing shear in shearsensitive fluids. A peristaltic pump mostly uses rollers to squeeze,occlude, flexible tubing against a pressure shoe forcing fluid to movebetween rollers. It is generally assumed in the art that it is verydifficult to achieve accurate, repeatable precision dispensing with thistype of pump due to roller progression, We have found that this is trueexcept where each cycle can be repeated with the rollers in the sameplace for the start of a dispense. This is usually one completerevolution of the pump or when a roller is in the same position at theend of a dispense cycle. The cyclic nature of roller progression ofperistaltic pumps is shown FIGS. 1A-1B. The results indicate a cyclicnature of the peristaltic pump system where the rollers progress foreach dispensing cycle. This is shown in FIGS. 1A-1B. Testing of thethree roller system, as shown in FIG. 1A, shows that with each 180degree index of the pump, there are two groups of weight determinations.

Complete and rotations indicate that the pump repeats very accurately asroller progression has been removed from FIG. 3. Looking at FIG. 1A, itcan be seen that the cycle repeats for approximately every 21 cycles. Ifthe rollers are located at any additional fraction of a completerotation, roller control is needed so that for each dispense the rollercan start in the same position. It would be very advantageous to useroller control to achieve accurate dispensing with a peristaltic pump.

SUMMARY OF THE INVENTION

A peristaltic system of the present invention can be effectively usedfor accurate fluid dispensing in peristaltic pumps if roller control isused. Peristaltic pumps can be combined with pinch valves allowing adispense tube to be open while a source tube is blocked. When rollermovement is used to move the next roller to the same starting positionthe dispense pinch valve is closed and the source valve is opened. Afterdispenses and prior to exercising valves, a drip retention is usedmoving a fluid back from the dispensing tips so when the pinch valve isused the valve actuation safely moves the fluid in the tube. Uponreleasing the valve opening the tube to dispensing the fluid moves backto its earlier position. Shown in FIG. 4, is the valve conditions forvarious connections.

The present invention uses roller positioning where the each roller isproperly positioned so that each dispense cycle starts in the sameposition. The data for this dispensing with the rollers being in thesame original position shows that the precision and accuracy is lessthan 0.3% total whereas most conventional systems only report theprecision and accuracy at better than 1.0%. This also depends on thedispensing volume, tubing set and pump/motor being used. FIG. 5 showsroller positioning.

DESCRIPTION OF THE FIGURES

Attention is now directed to several drawings that illustrate featuresof the present invention:

FIG. 1 shows 3-Roller Pump Cycles.

FIG. 2 shows 4-Roller Pump Cycles.

FIG. 3 shows Half Index Cycles.

FIG. 4 shows a representative Valve Diagram

FIG. 5 shows a Four Roller Pump-Position Control.

FIG. 6 shows a Cole Parmer MiniFlex and Watson-Marlow 313 & 114 Pumps.

FIG. 7 shows a Lexium Motor and Watson-Marlow 114 Pump.

FIG. 8 shows a Lexium Motor Wiring Diagram.

FIG. 9 shows an External Sensor

FIG. 10 shows Portion Dispensing.

FIG. 11 shows Watson-Marlow 114 Rollers

FIG. 12 shows a pre-stretch system

Several drawings and illustrations have been presented to aid inunderstanding the present invention. The scope of the present inventionis not limited to what is shown in these figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Peristaltic pumps can accurately dispense fluids if roller control isused to position each roller to the same starting position for eachdispense. A motor is used to move the rotor containing the rollers. Inorder to index rollers to the next dispensing position, it is necessaryto close off the tube used to dispense fluid and open a source tube tothe pump so that a roller position can take place without fluiddispensing. A roller can be moved in either direction once the sourcetube is activated, and the dispense tube closed. The present inventionuses the forward motor direction so the each roller is moved in thedirection of an output of the system. This puts the tubing in the samedirection as a dispense move, and not the drip retention direction.

The present invention is designed so that upon each dispense, the numberof counts from a stepper motor or an encoder is known. External sensorssuch as proximity or optical sensors can also be used. A typical steppermotor is made by Lexium. This Lexium stepper motor has 51,200 microsteps per revolution which can be used in determining roller positions.Using a 4-roller pump, the number of steps between each roller is51,200/4 or 12,800 steps. Knowing the number of rollers, or by sensingeach roller in the system, the dispense count after subtracting fullrevolutions can be used to move the next roller into position.

Steps between roller repeat positions based on a Lexium motor with51,200 steps per revolution.

-   -   2 Roller Pumps—51,200/2=25,600 Steps between rollers    -   3 Roller Pumps—51,200/3=17,066.667    -   4 Roller Pumps—51,200/4=12,800    -   6 Roller Pumps—51,200/6=8,533.33333    -   8 Roller Pumps—51,200/8=6,400    -   10 Roller Pumps—51,200/10=5,120    -   16 Roller Pumps—51,200/16=3,200

If a 4-roller pump is used, the progression can be up to 12,800 stepsfor each dispense. If 12,800 steps, or and even multiple that is beingused for each dispense, then there is no roller correction. Otherwise,for example, assume that the total dispense amount is 288,800 steps fora 4-roller pump. Knowing this value, the next roller can be advanced tothe same roller position as in the previous cycle by moving 12,800micro-steps. Thus, 288,800/12,800=22.5625 roller moves. Discarding thefull roller moves, the fraction is 0.5625 or 7200 steps beyond theroller start position. With 12,800 steps between rollers—7,200 is equalto 5,600 steps to bring the next roller into the same start position. Ifthe number of rollers does not divide into the 51,200 possible motormicro-steps evenly, then another calculation can be made. Assume thatthe pump has three rollers, or 17,066.667 steps between each roller. Thecalculation is made with 17,066 steps for the first two dispensepositions, and then the last move is for 17,068 steps making the stepcount of 17,066+17,066+17,068=51,200 or one complete motor revolution.

While the preferred motor is a stepper motor, any type of motor may beused including a linear motor or solenoid or other type of actuator.

The pump system also needs to have valve control so that dispense andsource valves can be actuated. The use of Lexium motors, the smartmotors have input and output built into the motors and can be programmedto operate the pump system correctly. The following sequence is used foraccurate dispensing:

1. The pump system is primed allowing all the tubes to fill with thedispensing fluid. First the dispensing leg of tubing is primed, and thenthe source tubing. This also allows the tube to “wear in” if a new tubeis being used.

2. The “Z” pulse of the encoder is found, and the motor is stopped. Eachmotor has a different “Z” pulse as the motor shafts are not registeredto a known position.

3. A step offset from this position is used for the starting point ofeach dispense. Usually this is at the 10:00 position for the roller, butmay be different based on pump type.

4. Several dispenses are made before a weight determination is made.After these dispenses, a single dispense is made and the weightdetermined. Specific gravity must be known for each fluid. This isrepeated several times, and an average is determined where by thecorresponding steps can be assigned.

5. The valve(s) are set without excitation with the dispensing valveopen and the source valve closed.

6. A drip retention is selected where the fluid is reversed resulting ina movement of the fluid back from the end of the output nozzle. Thisdrip retention is also automatically entered into the dispensecalculation.

7. The first dispense has the valves in the not excited values, and atthe end of the drip retention, each of the valves is actuated where thedispense valve is closed and the source valve opened.

8. A several dispenses are made before a weight verification is madeassuring that the system is setup correctly.

Roller control can be used with various pumps and tubing sets as shownin the following examples where a MiniFlex pump, (left view) from ColeParmer is used along with Watson-Marlow 313 and 114 pumps (right view).Other pumps and tubing can use the technology.

The system should be wired so that once the computer is removed, atrigger signal can used to the I/O to exorcise each dispense cycle(however, direct computer control of the motor position is within thescope of the present invention). The motor output needs to trigger aopto-amplifier which can handle the current necessary for each of thevalve actuations. In the configurations shown in FIG. 5, the motor iscoupled to the pump using a Helical coupler allowing a small amount ofmisalignment while not allowing rotational slip. FIG. 7 shows the modelfor the 100 system.

The Lexium motor was programmed through the RS485 port using customLexium code.

FIG. 8 is a wiring diagram for an embodiment of the present invention.

Roller control can be accomplished using external sensors such as aBanner reflector sensor as shown in FIG. 9. The sensor can count thenumber of rollers in a given system and then position rollers fordispensing.

Using roller control, a peristaltic pump can also be used as a “softwalled syringe pump” if the portion of the pump where the roller meetsthe pressure shoe has enough fluid volume. A Watson-Marlow 520 pumpsystem can demonstrate the use of pulsation free dispensing while theroller is in contact with the pressure shoe. The 520 pumps use tworollers that come in contact with the pressure shoe. Preferred tubeinternal diameters showing volumes using 0.005 tube diameter for 0.0 to0.02 ml, 0.008 diameter for 0.0 to 0.05 ml, 1.6 tube diameter for 0.0 to0.2 ml, 4.8 tube diameter for 0.0 to 1.6 mL and 8.0 tube diameter for0.0 to 4.5 mL. In FIG. 10, a 1.6 mm internal diameter silicon tube canbe seen for one full revolution of the pump. The curve represents 5dispensing cycles where points 1 through 7 can be used for a 0.02 mLpump. Linear pumps can be effectively used for this application.

Pulsation reduction can be achieved by adding more custom rollers to thepump rotor as the sixteen roller 313 Watson-Marlow pump, or the eightrollers to a 114 pump. A drawing of the pump is shown in FIG. 11. Therotors containing the rollers are made of aluminum and manufactured inone CNC Lathe setup. FIG. 11 shows a peristaltic pump 100 that containsa motor 103 and a shaft encoder 104. The motor 103 can turn a set ofrollers 101 by turning its central rotor or shaft 102. FIG. 11 showssets of four, six and eight rollers.

SUMMARY OF FEATURES

Some of the features of the present invention can be summarized asfollows:

A precision fluid dispensing system that includes a peristaltic pumpwith two or more rollers mounted on a rotor configured to execute asequence of single dispenses; a motor rotationally driving at a rotorcontaining the rollers; an encoder or external sensor cooperating withthe rotor so that the encoder or external sensor determines an absolutecircumferential position of the rollers with respect to the tubing.After each single dispense in the sequence of single dispenses, themotor positions the next roller to a position that has an identicalangular position with respect to the tubing as the previous roller hadbefore the dispense. The fluid dispensing system is set up so that eachsingle dispense represents one movement of one of the rotor (pressingone of the rollers against the tubing). The precision fluid dispensingsystem is set up so the sequence of single dispenses along with anoptional partial dispense results in a total dispense of a predeterminedquantity of fluid. In this present invention, if a stepper motor isused, the stepper motor has a fixed number of micro-steps perrevolution; each peristaltic pump has a fixed number of driven rollers,and the number of micro-steps in a single dispense equals the number ofmicro-steps per revolution divided by the number of driven rollers whenthis is an integer. In the present invention, if a stepper motor isused, the optional partial dispense has a number of micro-steps equal tothe total number of steps required for the total dispense modulo thenumber of steps in a single dispense. Finally, when the number ofmicro-steps per motor revolution divided by the number of rollers is notan integer, the number of micro-steps in each single dispense is thenumber of micro-steps per revolution divided by the number of rollerstruncated to the next lower integer for each single dispense except thelast single dispense in a motor revolution, with the last singledispense in the motor revolution containing a number of micro-stepsneeded to bring the total number of micro-steps per motor revolution tothe fixed number of micro-steps per revolution.

Parent U.S. Pat. No. 9,567,993 describes a way of holding the tubingduring a dispense operation. The present invention adds a second motorand a second encoder in order to access the exact amount of stretch inthe tubing. Optionally, in place of a motor, a negator spring may alsobe used with the encoder. This method is simpler and cheaper since theuse of a motor requires a custom motor and encoder assembly; however, amotor with encoder is typically more accurate and controllable. A thinmotor such as the Nanotec STF2818 requires extending the 3 mm shaft fromthe rear, attaching the second encoder thus making a custom motorassembly.

A negator spring can be used in conjunction with an encoder. With asimple negator spring as the top cover to the peristaltic pump, anencoder can read the negator spring advancement. The encoder can beadded to the system using simple gearing directly on the outside of aholding device, or directly on the holding shaft, for example, a NanotecCL3 encoder. In the case of a custom roller position motor/encoder, theencoder can be attached to the roller position controller eitherdirectly, or using a processor such as a Programmable Logic Controller(PLC).

Marprene tubing is in common use with peristaltic pumps throughoutindustry. However, the use of Marprene tubing requires stretching thetube a second time before commencing accurate dispensing. The encodercan indicate when the stretching of Marprene tubing for the second timeis necessary (using a second period of dispenses). The encoder alsoindicates the start of a peristaltic run, and when tubing needs to bechanged. The encoder in this case can determine the amount of stretchthe tubing has undergone.

In any roller peristaltic system, there is a degrading of the fluidoutput slope in milliliters due to tubing stretch. The output of theencoder can offset the roller starting position to compensate for thisstretch. In other words, the encoder can detect the amount of tubingstretch and compensate by adjusting the roller start positioning whichbecomes a new roller starting point. As previously stated, the systemcan be controlled by a PLC by connecting the hold device encoder to theroller starting position. The PLC both drives the motors in the systemand reads the encoder.

To begin the process, the tubing is loaded into the peristaltic pump.Tubing can chosen from various tube types of tubing including siliconand marprene tubing. Marprene tubing takes much longer to stretch, butthe present invention records the tube stretch and adjusts accordingly.The installed tubing typically has an unknown stretch. The cycle beginswith the secondary motor used to provide enough torque to prevent thesmaller tubing from going through a set of one way clutch rollers at theoutput of the pump.

The secondary motor outputs ample torque to create a force equal to theforce of the negator springs. This one-way clutch motor has a stretchencoder (second encoder) attached to track the stretch. Once the encoderindicates that the tube stretch is showing a sign of limited to nochange, the primary motor starts.

After one dispense sub-cycle, the volume is known from an independentweight scale and stored in memory. If an automated system is being used,the weight system is automatically seen at the PLC, and an adjustment asmade to the roller position. The primary motor then makes a drop suctionthat is adjusted to account for the tubing size. Once the tubingsuck-back takes place, the pump output is closed using a first solenoid.The tubing to the waste or supply tank is then opened by a secondsolenoid. The tube roller for the next roller position is adjusted tothe correct position based on volume, and the process repeats.

This process is continued for each tubing type that is used. and a tableis created and stored in memory. Marprene tubing undergoes a lengthytransformation, but if it is tied to a check weight system (a scale thatrecords weight of the dispense), the system can undergo a repositioningto compensate. The cycle continues until the stretch encoder indicates achange that is indicative of a tubing change. If the tubing is shiftedor replaced the calibration cycle repeats. If a weight check system isused, automatic weights can be loaded into the PLC or processor memoryand corrected by entering, or reading on the encoder, the rollerpositioning. If not, then a user must manually enter the weights.

Embodiments of the present invention add a second (or first) encoder tothe holding rollers to indicate when the initial tubing stretch iscomplete. If the tubing undergoes continuing stretching such asMarprene, the invention uses the encoder to reposition the next roller.In the case of silicon tubing, there is only an initial stretch which isseen by the holding clutches and encoder, so it is known when to start arun. If the tubing wears out after extensive run dispenses, the encoderindicates this, and notifies the user to change the tubing.

FIG. 12 shows a block diagram of a pre-stretch system. A primary motor207 drives a peristaltic pump 201. A first encoder 200 is attached tothe shaft of the primary motor 207. The primary motor 207 and firstencoder 200 are both in communications with a processor such as a PLC206. A secondary motor 202 is set up to stretch the tubing with a secondencoder 203 that measures tubing stretch. A return solenoid 204 andoutput solenoid 205 control the pinch valves previously described. Thesecondary motor 202, second encoder 203 and the solenoids 204, 205 arealso in communication with the processor or PLC 206. The PLC controlsthe pre-stretch process, controls the primary motor during dispense,records weights and makes roller position adjustments to compensate forweight errors and keep the dispense on target. The processor or PLC 206has memory that can be disk, random access (RAM), read-only (ROM) andcan optionally communicate on a network allowing remote control, remoteupdating and remote monitoring. The network can be wired or wireless. Inparticular it can be radio such as WiFi or any other network. Thecommunications paths shown in FIG. 12 can be separate from the network(if one is used), or they can be part of the network.

Again, the stretch compensation process is as follows (a secondaryencoder indicates stretch):

-   -   1. First the initial tubing stretch occurs under control of a        secondary motor. This requires a first, and possibly a second or        additional cycles in order to settle the clutch output encoder        signal so that the controller knows that the initial stretch is        complete.    -   2. Once the initial stretch has completed. a signal is provided        to the primary motor, or to a PLC that controls the primary        motor indicating that the system can proceed with a dispense. A        full dispense usually requires several dispense sub-cycles and        possibly a partial dispense sub-cycle.    -   3. A dispense sub-cycle is made, and the amount of fluid        dispensed of the particular type of fluid being used is        determined by a weight scale, or within a special tube that has        a check weigh system attached to the tube. The encoder reports        primary motor shaft positions to the PLC system.    -   4. The next step is a drip reversal. The amount of reversal of        fluid is selected to compensate for the output pinch valve        output closure.    -   5. With the output pinch valve closed, another valve to the        waste depository or the return to the supply container is        opened. These two valves are typically controller by solenoids        under control of the processor or PLC.    -   6. The roller is then moved by the primary motor to the correct        roller position for the next dispense sub-cycle. Subsequent        repositioning of the roller can be made in either direction to        minimize waste. The roller position can be determined by a        separate encoder (first encoder) on the primary motor or on the        roller shaft.    -   7. The return to waste pinch valve is closed and the output        pinch valve is opened.    -   8. The dispense process continues with a dispense cycle or        sub-cycle.    -   9. Each new roller repositioning can have a small volume        adjustment to keep the dispensing volume on its target by a        continuous check weight system on the check weight scale. This        information is reported to the primary motor control function of        the PLC. This compensates for tubing stretch and other error        factors.    -   10. The dispense cycles or sub-cycles continue until a full        dispense is complete.    -   11. A series of full dispenses can be made until the holding        tubing encoder begins to report an expansion in counts        indicating tubing weakening, excessive stretch or complete        tubing failure, each of which indicating that tubing needs to be        replaced or at least shifted in position.

Summary of the Basic Dispense Cycle or Sub-Cycle

The system has a peristaltic pump with N rollers on a rotor, where N isa positive integer, and a primary motor driving the rotor. An encodercooperates with the rotor determining the rotational position of therotor. A deformable tube passes through the peristaltic pump connectedat a first end to a fluid source and connected at a second end to adispense point. This tube passes through a first pinch valve locatedbetween the fluid source and the peristaltic pump, and passes through asecond pinch valve located between the peristaltic pump and the dispensepoint. The system makes a precision fluid dispense by:

a) opening the first pinch valve, closing the second pinch valve, androtating the rotor to draw fluid into the deformable tube.

b) closing both the first and second pinch valves and rotating the rotorto a predetermined relative dispense starting angular positiondetermined by the first encoder;

c) closing the first pinch valve, opening the second pinch valve, androtating the rotor a predetermined number of degrees determined by thefirst encoder to dispense a predetermined amount of fluid;

d) moving the rotor a predetermined amount in an opposite direction toprevent a drip;

The system performs subsequent dispenses by executing steps a), b), c)and d) in order always bringing the rotor to the same predeterminedrelative angular dispense position determined by the first encoder instep b). The predetermined relative angular dispense position is reachedby moving the rotor until one of the N rollers is at a predeterminedangle with respect to a vertical direction. This predetermined angleallows each subsequent dispense to start with the rotors in the samegeometric positions (the one roller at the predetermined angle will manytimes be a different roller, but the geometric pattern is the same. Forexample, if the first dispense starts with one roller at 10 degrees offvertical, every subsequent dispense will start with at least one of therollers 10 degrees off vertical).

As discussed, new tubing needs to be pre-stretched. The presentinvention does this with a secondary motor and second encoder attachedto it or to a negator spring that can be attached to the peristalticpump. The pre-stretch can be repeated one or through a plurality ofdispense cycles until the second encoder indicates that stretching hasreached a minimum or a predetermined amount. In the case of silicontubing, the stretching will reach a minimum; in the case of Marprenetubing, the pre-stretch will be up to a predetermined amount (Marprenetubing keeps stretching in use, where silicon and other tubing typicallydoes not, or at least only a very small amount). In any case, theprocessor can keep track of the stretch during use, and as stated,notify the user when the tubing has stretched beyond its useful life.

As discussed, the predetermined angular start position can have a smallangular adjustment to achieve a small volume adjustment to keep thedispensing volume to a predetermined amount or target value.

Several descriptions and illustrations have been presented to aid inunderstanding the present invention. One with skill in the art willrealize that numerous changes and variations may be made withoutdeparting from the spirit of the invention. Each of these changes andvariations is within the scope of the present invention.

We claim:
 1. A precision fluid dispensing system comprising: aperistaltic pump with N rollers on a rotor, where N is a positiveinteger; a primary motor driving the rotor; a first encoder cooperatingwith the rotor, the first encoder adapted to determine a rotationalposition of the rotor; a deformable tube passing through the peristalticpump connected at a first end to a fluid source and connected at asecond end to a dispense point; the deformable tube passing through afirst pinch valve located between the fluid source and the peristalticpump; the deformable tube also passing through a second pinch valvelocated between the peristaltic pump and the dispense point; the systemconstructed to make a precision fluid dispense by a) opening the firstpinch valve, closing the second pinch valve, and rotating the rotor todraw fluid into the deformable tube; b) closing both the first andsecond pinch valves and rotating the rotor to a predetermined relativedispense starting angular position determined by the first encoder; c)closing the first pinch valve, opening the second pinch valve, androtating the rotor a predetermined number of degrees determined by thefirst encoder to dispense a predetermined amount of fluid; d) moving therotor a predetermined amount in an opposite direction to prevent a drip;wherein, the system is constructed to perform subsequent dispenses byexecuting steps a), b), c) and d) in order always bringing the rotor tothe same predetermined relative angular dispense position determined bythe first encoder in step b), and wherein the predetermined relativeangular dispense position is reached by moving the rotor until one ofthe N rollers is at a predetermined angle with respect to a verticaldirection.
 2. The precision fluid dispensing system of claim 1 whereinthe sequence of single dispenses, along with an optional partialdispense, results in a total dispense of a predetermined quantity offluid.
 3. The precision fluid dispensing system of claim 1 furtherincluding a scale that determines weight of a dispensing volume of fluidin a single dispense.
 4. The precision fluid dispensing system of claim3 wherein the scale determines the weight of each dispense.
 5. Theprecision fluid dispensing system of claim 1 wherein the primary motoris a stepper motor that has a fixed number of micro-steps perrevolution; the peristaltic pump has a fixed number of rollers on thedriven rotor, and the number of micro-steps in a single dispense equalsthe number of micro-steps per revolution divided by the number ofrollers.
 6. The precision fluid dispensing system of claim 1 furthercomprising a secondary motor with a second encoder attached to thedeformable tube constructed to pre-stretch deformable tube beforedispensing begins.
 7. The precision fluid dispensing system of claim 6wherein said pre-stretch is repeated through a plurality of dispensecycles until the second encoder indicates that stretching has reached aminimum or a predetermined amount.
 8. The precision fluid dispensingsystem of claim 4 wherein the predetermined angular start position has asmall angular adjustment to achieve a small volume adjustment to keepthe dispensing volume to a predetermined amount.
 9. The precision fluiddispensing system of claim wherein a total dispense includes a pluralityof single dispenses; the primary motor being a stepper motor having afixed number of micro-steps per revolution, and the peristaltic pumphaving a fixed number of rollers; and wherein, the number of micro-stepsper revolution divided by the number of rollers is not an integer, thenumber of micro-steps in each single dispense is the number ofmicro-steps per revolution divided by the number of rollers truncated tothe next lower integer for each single dispense, except for a lastsingle dispense, with the last single dispense containing a number ofmicro-steps needed to bring a total number of micro-steps in the totaldispense to the fixed number of micro-steps per revolution.
 10. A methodof making a precision fluid dispense with a peristaltic pump system, theperistaltic pump system having peristaltic pump with a primary motordriving a rotor with N rollers, where N is a positive integer, a firstencoder on the rotor; a deformable tube running from a fluid source,passing through the peristaltic pump, and running to a dispense point,the method comprising: a) drawing fluid into the deformable tube byrotating the rotor; b) rotating the rotor so that the nth roller is at apredetermined dispense starting angle determined by the encoder, where nis a positive integer greater than or equal to 1 and less than or equalto N c) making a partial dispense by rotating the rotor through adispense angle determined by the encoder causing only the nth roller topinch the deformable tube; d) closing a pinch valve on the deformabletube located between the peristaltic pump and the dispense point; e)rotating the rotor so that the n+1 roller is at the predetermineddispense starting angle determined by the encoder, where n+1 is apositive integer greater than or equal to 1 and less than or equal to N,and is n+1 is greater than n by one unless n=N, wherein if n=N, n+1=1;f) opening the pinch valve; g) letting n become n+1; h) repeating stepsb) through g) until a predetermined total dispense of fluid has takenplace.
 11. The method of claim 10 wherein a second motor with a secondencoder pre-stretches the deformable tube before dispensing starts.